1. Field of the Invention
This invention generally relates to shipping drums and, more particularly, to seals for resisting leakage of materials from such drums, particularly during transport.
2. Description of Related Art
It is well known to store and transport materials, particularly of the hazardous type that are toxic by inhalation, in shipping drums of substantial capacity, e.g. on the order of 55 gallons. To minimize the risk of leakage associated with the transport of such toxic materials, the drums are typically provided with threaded closures that are adequately torqued and tightened. Nevertheless, no matter how much tightened, the closure has a tendency to back up and loosen, at least to a certain extent, due to vibrations and impact forces commonly experienced during shipping of the toxic materials. Where materials of ever-increasing toxicity are concerned, even an ever-so-slight deterioration of integrity of the drum seal is not acceptable and must be prevented.